Nox1 serves as the catalytic core of a multi-subunit NADPH oxidase enzyme complex, which assembles in response to signaling cascades initiated by mechanical stress, cytokines and growth factors. Nox1 is a transmembrane protein expressed in multiple tissues including vascular smooth muscle cells (VSMCs), brain, gastrointestinal epithelium, and prostate tumor cells (Fukui et al., 1995; Reinehr et al., 2007; Rokutan et al., 2006; Lim et al., 2005). Nox1 plays a critical role in the development of cardiovascular disease (CVD), amyotropic lateral sclerosis (ALS), gastrointestinal disease, immunological disorders, and multiple forms of cancer (Leto and Geiszt, 2005; Lambeth, 2004; Sumimoto et al., 1994).
Since its discovery in 1999, multiple studies have provided evidence that activation of Nox1 is a multi-step process that requires assembly of a complex of proteins (Lassegue et al., 2012). Nox1 associates with the transmembrane protein p22phox for stability and membrane localization. The recruitment of cytosolic proteins to the membrane forms a complex which allows electron transfer from NADPH to oxygen to form superoxide (Hanna et al., 2004; Banfi et al., 2003; Lambeth, 2004). When activated, the organizer cytosolic protein p47phox or its homolog NoxO1 tethers to p22phox (Huang et al., 1999; Debbabi et al., 2013; Kawahara et al., 2005). Recruitment of the activator p67phox or its homolog NoxA1 is mediated via tail-to-tail binding to the organizer protein (Huang et al., 1999; Debbabi et al., 2013; Kawahara et al., 2005). Mutation of the “activation domain” of NoxA1 abrogates Nox1-generated ROS (Maehara et al., 2010). However, the molecular interaction of Nox1 with the activation domain of NoxA1 is not known. Phosphorylation of NoxA1 allows for dissociation from Nox1 and is one mechanism to terminate enzyme activity (Kobayashi et al., 1989). Whether post-translational modifications of Nox1 regulate its activation has not been explored.